As size of patterns is rapidly decreased in accordance with miniaturization and high integration of semiconductor devices, a collapse phenomenon of photoresist patterns has emerged as the hardest part during processes, and accordingly, it is inevitable that a thickness of a photoresist film and patterns becomes gradually thinner to achieve a high resolution image. However, since it is difficult to etch a material layer to be etched by using patterns formed with a thinner photoresist, an inorganic or organic film having strong etching resistance is introduced between the material layer and the photoresist. This inorganic or organic film refers to an underlayer film or a hardmask, and a hard mask process refers to a general process of etching the hard mask using the photoresist patterns to perform patterning, and etching the material layer using the patterns of the hard mask. Inorganic underlayer film used for the hard mask process is made of polysilicon, silicon nitride, silicon oxynitride, titanium nitride, amorphous carbon, etc., and is conventionally formed by chemical vapor deposition (CVD).
The hard mask formed by the chemical vapor deposition has good physical properties in view of etching selectivity or etching resistance, but has problems such as particle occurrence, void occurrence in a part having large steps, etc., particularly, high investment cost for initial equipments. In order to solve these problems, a need for developing a spin-on hard mask composition that is easily capable of performing spin-coating using a track system used in a photolithography process in a semiconductor line instead of using the deposited hard mask emerged, and development of specific materials for solving these problems has been attempted. The hard mask (spin-on hard mask) formed by the spin-coating has difficulty in obtaining the same etching resistance as the hard mask formed by CVD process. However, the hard mask formed by the spin-coating has advantages in that it is easier to form a thin film by a solution stage of coating, and coating uniformity and roughness of thin film surface are improved, etc. In addition, the initial investment cost of the hard mask formed by the spin-coating is less than that of the hard mask formed by a CVD process.
As described above, the recent trend of miniaturization of a lithography process according to continuous integration of LSI (large scale integrated circuit) has reached the limit for being implemented as an argon fluoride immersion lithography photoresist which is the top in the existing photoresist. In particular, in order to perform an ultrafine patterning process of 30 nm node or less, resolution of the photoresist used in the lithography process functions is an important factor. However, since the existing photoresist has a limitation in implementing patterns of 30 nm or less, development of a novel additional process has been attempted to overcome the limitation.
Technologies that are practically applied among a number of currently developed technologies are mainly a double patterning method in which primary and secondary exposure processes and an etching process are performed and a double patterning process (SPT, Spacer Patterning Technology) using a spacer, and materials used as a hard mask in the additional process commonly refer to an underlayer film composition. It is noted that in addition to the use of amorphous carbon as a hard mask, the used amount of the underlayer film composition has been rapidly increased as a novel hard mask material in a situation in which the double patterning process which is a process for implementing new high resolution generally leads ArF lithography process. The largest physical properties that are required for the underlayer film include high etching resistance, thermal stability, excellent solubility to general organic solvents, storage stability, adhesion property, and excellent coating uniformity, etc. The reason for requiring thermal stability is that an underlayer film is formed, and then, a vacuum deposition process at high temperature is performed on an upper part thereof as a subsequent process, wherein in view of heat resistance, low decomposition of a polymer at 400° C. and a film decrease by 5% or less are generally required for a stable vacuum deposition process. The etching resistance is another factor that is significantly important for etching a substrate while having the minimum thickness as the underlayer film. The reason is because as a thickness of the film is increased, risk that patterns may naturally collapse during the process is increased. The etching resistance is favorable as carbon content of a polymer is high, but it is preferred that the carbon content of the polymer is 82% or more in consideration of solubility to a solvent, coating uniformity, etc.
In the related art, polymers having high carbon content and polarity and high thermal stability have been mainly studied as a polymer material in a composition in order to satisfy characteristics of the underlayer film material, and in particular, polyamide, polyetheretherketone, polyaryl ether, other phenolic polymers, etc., have been variously studied. It was confirmed that some of the polymers had sufficient high-temperature stability and a film-forming ability. However, when polymers have desired level of carbon contents related with etching resistance, the polymers have problems in view of storage stability, line compatibility, and coating uniformity due to rapid decrease in solubility. When polymers have insufficient heat resistance, the polymers have a problem in that a gas emission amount is large during the process due to low thermal stability.
That is, physical properties of the underlayer film composition are dependent on characteristics of the polymer. In particular, thermal stability and etching resistance in the characteristics of the polymer are intactly reflected in the characteristics of the underlayer film composition. The thermal stability is dependent on stability of a polymer main chain, and the etching resistance is excellent as a carbon content present in the polymer is high. On the contrary, as the number of hetero elements such as oxygen or nitrogen is increased, the etching resistance is decreased. The thermal stability is dependent on a chemical structure and bond strength of the polymer. In particular, the number of compounds of which stability is maintained at a temperature of 400° C. or more is small. Examples of the polymer having excellent thermal stability may include polyimide, polyamide, polyarylketone ether, etc. However, the polymers having excellent thermal stability have limitation in being used as the underlayer film material since etching resistance is decreased or solubility with respect to general organic solvents is low.
In addition, surface planarization and uniformity of pattern edges may be controlled by a molecular weight of the polymer or an additive. Other mechanical properties of the pattern are also determined by kinds and structures of the polymer.